Waveguide architecture for photonic neural component with multiplexed optical signals on inter-node waveguides

ABSTRACT

A photonic neural component including optical transmitters, optical receivers, inter-node waveguides formed on a board, multiplexers configured to multiplex input optical signals onto the inter-node waveguides, transmitting waveguides configured to receive optical signals emitted from the optical transmitters and transmit the received optical signals to the inter-node waveguides via the multiplexers, mirrors to partially reflect optical signals propagating on the inter-node waveguides, receiving waveguides configured to receive reflected optical signals produced by the mirrors and transmit the reflected optical signals to the optical receivers, and filters configured to apply weights to the reflected optical signals. The transmitting waveguides and receiving waveguides are formed on the board such that one of the transmitting waveguides and one of the receiving waveguides crosses one of the inter-node waveguides with a core of one of the crossing waveguides passing through a core or clad of the other.

BACKGROUND Technical Field

The present invention generally relates to a waveguide architecture fora photonic neural component, and more particularly to a waveguidearchitecture for a photonic neural component of a neural network.

Related Art

Non-traditional, neuromorphic computing architectures, such as neuralnetworks and reservoir computing, have shown promise in terms ofperformance, but conventional electronic approaches to interconnectingneurons have met with some limitations. For example, the IBM TrueNorthsystem operates with a processing speed in the kHz range due to the needfor time multiplexing. Recently, excitable opto-electronics devices havegenerated interest as a way of potentially lifting this speedlimitation. (See, for example, A. N., Tait et al., “Broadcast andWeight: An Integrated Network For Scalable Photonic Spike Processing,”J. Light. Tech. 32, 3427, 2014, M. A. Nahmias et al., “An integratedanalog O/E/O link for multi-channel laser neurons,” Appl. Phys. Lett.108, 151106 (2016), and K. Vandoorne et al., “Experimental demonstrationof reservoir computing on a silicon photonics chip,” NatureCommunication 5, 3541, 2014). However, such attempts have been limitedby very high power consumption and optical loss. Meanwhile, thefabrication of waveguide crossing structures with very low loss hasrecently become possible. (See, for example, N. Bamiedakis et al., “LowLoss and Low Crosstalk Multimode Polymer Waveguide Crossings forHigh-Speed Optical Interconnects,” 2007 Conference on Lasers andElectro-Optics (CLEO), CMG1).

SUMMARY

In accordance with an embodiment of the present invention, a photonicneural component capable of overcoming the above drawbacks accompanyingthe related art is provided. The photonic neural component includes aplurality of optical transmitters, a plurality of optical receivers, aplurality of inter-node waveguides formed on a board, a plurality ofmultiplexers formed on the board, each multiplexer configured tomultiplex an input optical signal onto an inter-node waveguide of theplurality of inter-node waveguides, a plurality of transmittingwaveguides formed on the board such that at least one of thetransmitting waveguides crosses at least one of the inter-nodewaveguides with a core of one of the crossing waveguides passing througha core or a clad of the other, each transmitting waveguide opticallyconnected to an optical transmitter of the plurality of opticaltransmitters and configured to receive an optical signal emitted fromthe optical transmitter and transmit the received optical signal to aninter-node waveguide of the plurality of inter-node waveguides via amultiplexer of the plurality of multiplexers, a plurality of mirrorsformed on the board, each mirror to partially reflect an optical signalpropagating on an inter-node waveguide of the plurality of inter-nodewaveguides to provide a reflected optical signal, a plurality ofreceiving waveguides formed on the board such that at least one of thereceiving waveguides crosses at least one of the inter-node waveguideswith a core of one of the crossing waveguides passing through a core ora clad of the other, each receiving waveguide optically connected to anoptical receiver of the plurality of optical receivers and configured toreceive a reflected optical signal produced by a mirror of the pluralityof mirrors and transmit the reflected optical signal to the opticalreceiver, and a plurality of filters formed on the board, each filterconfigured to apply a weight to a reflected optical signal produced by amirror of the plurality of mirrors before the reflected optical signalis transmitted to an optical receiver by the receiving waveguide thatreceives the reflected optical signal. The photonic neural component maysupport design flexibility while lifting the speed restriction of theconventional electronic approach.

In accordance with an embodiment of the present invention, the pluralityof optical transmitters may include a first optical transmitter thatemits an optical signal at a first wavelength and a second opticaltransmitter that emits an optical signal at a second wavelengthdifferent from the first wavelength, and the inter-node waveguides mayinclude an inter-node waveguide that propagates the optical signal atthe first wavelength and the optical signal at the second wavelength.The plurality of mirrors may include a mirror whose reflectioncoefficient depends on wavelength. The plurality of filters may includea spectral filter whose applied weight depends on wavelength. A photonicneural component with these features may support wavelength divisionmultiplexing (WDM) of optical signals on the inter-node waveguides,reducing the number of inter-node waveguides necessary.

In accordance with an embodiment of the present invention, the pluralityof multiplexers include a multiplexer having an entrance mirror and ay-shaped waveguide structure connected by a first entrance arm and anexit arm to the inter-node waveguide onto which the multiplexermultiplexes its input signal, the entrance mirror configured to receive,as the input signal, an optical signal transmitted by a transmittingwaveguide of the plurality of waveguides and reflect the input signal toproduce a reflected optical signal that enters a second entrance arm ofthe y-shaped waveguide structure and joins an optical signal propagatingon the inter-node waveguide where the second entrance arm meets thefirst entrance arm of the y-shaped waveguide structure. The photonicneural component may support multiplexing of optical signals on theinter-node waveguides, thereby reducing the number of inter-nodewaveguides necessary.

In accordance with an embodiment of the present invention, the pluralityof filters include an exchangeable filter that can be exchanged tochange the applied weight. The photonic neural component may supporttuning of a neural network comprising the photonic neural component.

In accordance with an embodiment of the present invention, the pluralityof filters include a variable filter whose transparency can be varied tochange the applied weight. The photonic neural component may supporttuning of a neural network comprising the photonic neural component.

In accordance with an embodiment of the present invention, the photonicneural component further includes a plurality of semiconductor chipsmounted on the board, each of the semiconductor chips including at leastone of the optical transmitters or at least one of the opticalreceivers. The photonic neural component may further support designflexibility.

In accordance with an embodiment of the present invention, the pluralityof semiconductor chips include optical transmitter chips and opticalreceiver chips, each of the optical transmitter chips including one ormore of the optical transmitters and each of the optical receiver chipsincluding one or more of the optical receivers, and the opticaltransmitter chips include a first optical transmitter chip whose one ormore optical transmitters emit optical signals at a first wavelength anda second optical transmitter chip whose one or more optical transmittersemit optical signals at a second wavelength different from the firstwavelength. Each of the optical transmitter chips include the samenumber of optical transmitters, each of the optical receiver chipsinclude the same number of optical receivers, the number of opticaltransmitters included in each of the optical transmitter chips may bethe same as the number of optical receivers included in each of theoptical receiver chips, and the number of inter-node waveguidesconnected to each of the optical transmitter chips via the transmittingwaveguides may be the same as the number of optical transmittersincluded in each of the optical transmitter chips and the number ofoptical receivers included in each of the optical receiver chips. Thephotonic neural component may support design flexibility andmultiplexing of optical signals on the inter-node waveguides, reducingthe number of inter-node waveguides necessary.

In accordance with an embodiment of the present invention, each of thesemiconductor chips can be arranged such that the at least one opticaltransmitter included in the chip or the at least one optical receiverincluded in the chip faces the board, the transmitting waveguides can beconnected to the optical transmitters via entry mirrors arranged toredirect light from a direction perpendicular to the board to adirection parallel to the board, and the receiving waveguides can beconnected to the optical receivers via exit mirrors arranged to redirectfrom a direction parallel to the board to a direction perpendicular tothe board. The photonic neural component may further support designflexibility by supporting the use of waveguides formed on the board.

In accordance with an embodiment of the present invention, the photonicneural component further includes a plurality of intra-node signallines, each intra-node signal line connected to an optical receiver ofthe plurality of optical receivers and an optical transmitter of theplurality of optical transmitters and configured to receive anelectrical signal representing a power of an optical signal received bythe optical receiver and transmit the electrical signal to the opticaltransmitter, thereby connecting the optical receiver and the opticaltransmitter to form an input and an output of a neuron. For each of theoptical receivers connected to an optical transmitter via an intra-nodesignal line, the plurality of mirrors include a mirror whose reflectedoptical signal is transmitted to the optical receiver and whosereflection coefficient is substantially zero for a wavelength of theoptical signal emitted by the optical transmitter. The photonic neuralcomponent may support functionality of the photonic neural component asa neural network or portion thereof.

In accordance with an embodiment of the present invention, theinter-node waveguides, the transmitting waveguides, and the receivingwaveguides may be made of polymer in a single layer of the board. Thephotonic neural component may support design flexibility while reducingoptical loss.

In accordance with an embodiment of the present invention, the pluralityof optical transmitters are divided into differential pairs in which oneof the optical transmitters of a differential pair emits a variableoptical signal while the other of the optical transmitters of thedifferential pair emits a reference optical signal. The photonic neuralcomponent may further include a plurality of semiconductor chips mountedon the board, each of the semiconductor chips including one or more ofthe differential pairs. Each of the semiconductor chips can include twoor more of the differential pairs. The photonic neural component maysupport functionality of the photonic neural component as a neuralnetwork or portion thereof.

In accordance with an embodiment of the present invention, the pluralityof inter-node waveguides includes a first ring having two or more of theinter-node waveguides arranged as concentric loops, the plurality ofoptical transmitters can include a first inner optical transmitter grouphaving two or more of the optical transmitters disposed inside the firstring, and the plurality of optical receivers can include a first inneroptical receiver group having two or more of the optical receiversdisposed inside the first ring. The photonic neural component maysupport input/output functionality and expandability of the photonicneural component as a neural network or portion thereof.

In accordance with an embodiment of the present invention, the pluralityof mirrors include a first mirror group, each mirror of the first mirrorgroup to partially reflect an optical signal propagating on aninter-node waveguide of the first ring to provide a reflected opticalsignal, and the photonic neural component may further include aplurality of first output waveguides formed on the board such that atleast one of the first output waveguides crosses at least one of theinter-node waveguides of the first ring with a core of one of thecrossing waveguides passing through a core or a clad of the other, eachfirst output waveguide connected to outside the first ring andconfigured to receive a reflected optical signal produced by a mirror ofthe first mirror group and transmit the reflected optical signal tooutside the first ring. The photonic neural component may furtherinclude a first output filter formed on the board, the first outputfilter configured to apply a weight to a reflected optical signalproduced by a mirror of the plurality of mirrors before the reflectedoptical signal is transmitted to outside the first ring by the firstoutput waveguide that receives the reflected optical signal. Theplurality of optical receivers can include a first outer opticalreceiver group having two or more of the optical receivers disposedoutside the first ring, each of the optical receivers of the first outeroptical receiver group connected to a first output waveguide of theplurality of first output waveguides and configured to receive thereflected optical signal transmitted by the first output waveguide. Theplurality of inter-node waveguides can include a second ring having twoor more of the inter-node waveguides arranged as concentric loops, theplurality of optical transmitters may include a second inner opticaltransmitter group having two or more of the optical transmittersdisposed inside the second ring and a second outer optical transmittergroup having two or more of the optical transmitters disposed outsidethe second ring, the plurality of optical receivers may include a secondoptical receiver group having two or more of the optical receiversdisposed inside the second ring, the plurality of multiplexers mayinclude a second multiplexer group, each multiplexer of the secondmultiplexer group configured to multiplex an input optical signal ontoan inter-node waveguide of the second ring, the photonic neuralcomponent may further include a plurality of second input waveguidesformed on the board such that at least one of the second inputwaveguides crosses at least one of the inter-node waveguides of thesecond ring with a core of one of the crossing waveguides passingthrough a core or a clad of the other, each second input waveguideoptically connected to an optical transmitter of the second outeroptical transmitter group and configured to receive an optical signalemitted from the optical transmitter and transmit the received opticalsignal to an inter-node waveguide of the second ring via a multiplexerof the second multiplexer group, and the plurality of intra-node signallines may include a plurality of inter-ring intra-node signal lines,each inter-ring intra-node signal line connected to an optical receiverof the first outer optical receiver group and an optical transmitter ofthe second outer optical transmitter group and configured to receive anelectrical signal representing a power of an optical signal received bythe optical receiver and transmit the electrical signal to the opticaltransmitter, thereby connecting the optical receiver and the opticaltransmitter to form an input and an output of a neuron. The photonicneural component may support input/output functionality andexpandability of the photonic neural component as a neural network orportion thereof.

In accordance with an embodiment of the present invention, the pluralityof multiplexers include a first multiplexer group, each multiplexer ofthe first multiplexer group configured to multiplex an input opticalsignal onto an inter-node waveguide of the first ring, and the photonicneural component further including a plurality of first input waveguidesformed on the board such that at least one of the first input waveguidescrosses at least one of the inter-node waveguides of the first ring witha core of one of the crossing waveguides passing through a core or aclad of the other, each first input waveguide connected to outside thefirst ring and configured to receive an optical signal from outside thefirst ring and transmit the received optical signal to an inter-nodewaveguide of the first ring via a multiplexer of the first multiplexergroup. The plurality of optical transmitters can include a first outeroptical transmitter group having two or more of the optical transmittersdisposed outside the first ring, each of the first optical transmittersof the first outer optical transmitter group optically connected to afirst input waveguide of the plurality of first input waveguides andconfigured to emit an optical signal to be transmitted by the firstinput waveguide. The plurality of inter-node waveguides can include asecond ring having two or more of the inter-node waveguides arranged asconcentric loops, the plurality of optical transmitters can include asecond inner optical transmitter group having two or more of the opticaltransmitters disposed inside the second ring, the plurality of opticalreceivers can include a second optical receiver group having two or moreof the optical receivers disposed inside the second ring and a secondouter optical receiver group having two or more of the optical receiversdisposed outside the second ring, the plurality of mirrors can include asecond mirror group, each mirror of the second mirror group configuredto partially reflect an optical signal propagating on an inter-nodewaveguide of the second ring to provide a reflected optical signal, thephotonic neural component can further include a plurality of secondoutput waveguides formed on the board such that at least one of thesecond output waveguides crosses at least one of the inter-nodewaveguides of the second ring with a core of one of the crossingwaveguides passing through a core or a clad of the other, each secondoutput waveguide optically connected to an optical receiver of thesecond outer optical receiver group and configured to receive areflected optical signal produced by a minor of the second mirror groupand transmit the reflected optical signal to the optical receiver, andthe plurality of intra-node signal lines may include a plurality ofinter-ring intra-node signal lines, each inter-ring intra-node signalline connected to an optical transmitter of the first outer opticalreceiver group and an optical receiver of the second outer opticalreceiver group and configured to receive an electrical signalrepresenting a power of an optical signal received by the opticalreceiver and transmit the electrical signal to the optical transmitter,thereby connecting the optical receiver and the optical transmitter toform an input and an output of a neuron. The photonic neural componentmay support input/output functionality and expandability of the photonicneural component as a neural network or portion thereof.

The summary clause does not necessarily describe all of the features ofthe embodiments of the present invention. The present invention may alsobe a combination or sub-combination of the features described above,including a combination of features from two or more of the aspectsdescribed above. The above and other features and advantages of thepresent invention will become more apparent from the followingdescription of the embodiments, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example schematic of a waveguide architecture for aphotonic neural component according to an embodiment of the presentinvention;

FIG. 2 shows an example schematic of a region of the waveguidearchitecture shown in FIG. 1.

FIG. 3 shows an example schematic of the waveguide architecture shown inFIG. 1 including reflection coefficients of mirrors;

FIG. 4 shows an example schematic of the region of the waveguidearchitecture shown in FIG. 2 including arbitrary weights of a filter;

FIG. 5 shows an example schematic side view of a portion of a board onwhich a transmitter chip and a transmitting waveguide are formed;

FIG. 6 shows an example schematic side view of a portion of a board onwhich a receiver chip and a receiving waveguide are formed;

FIG. 7 shows an example schematic of a waveguide architecture for aphotonic neural component according to an embodiment of the presentinvention; and

FIG. 8 shows an example schematic of a waveguide architecture for aphotonic neural component according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present invention will bedescribed. The embodiments should not be construed as limiting the scopeof the invention, which is defined by the claims. The combinations offeatures described in the embodiments are not necessarily essential tothe invention.

FIG. 1 shows an example schematic of a waveguide architecture for aphotonic neural component 100 according to an embodiment of theinvention. Using the waveguide architecture shown in FIG. 1, a photonicneural component 100 can support photonic spike computing by opticalsignal transmission with low loss via waveguides formed so as to crossone another on a board, e.g., a printed circuit board. The disclosedwaveguide architecture can, therefore, allow for design flexibility(e.g., layout, materials, etc.) while lifting the speed restriction ofthe conventional electronic approach. The photonic neural component 100includes a plurality of optical transmitter chips 110A to 110D, aplurality of optical receiver chips 120A to 120D, a plurality ofinter-node waveguides 130-1 to 130-4, a plurality of multiplexers 140Ato 140D, a plurality of transmitting waveguides 150A-1 to 150D-4, aplurality of mirrors 160A to 160D, a plurality of receiving waveguides170A-1 to 170D-4, a plurality of filters 180A to 180D, and a pluralityof intra-node signal lines 190A-1 to 190D-4. Due to limited space, outof the plurality of transmitting waveguides 150A-1 to 150D-4, onlytransmitting waveguides 150C-1 to 150C-4 are given reference numbers inFIG. 1. Similarly, out of the plurality of receiving waveguides 170A-1to 170D-4 only receiving waveguides 170C-1 to 170C-4 are given referencenumbers in FIG. 1, and out of the plurality of intra-node signal lines190A-1 to 190D-4 only intra-node signal lines 190A-1 to 190A-4 are givenreference numbers in FIG. 1. Nevertheless, the omitted reference numbersof transmitting waveguides, receiving waveguides, and intra-node signallines depicted in FIG. 1 may be referred to throughout this disclosurewith the understanding that the letter suffixes A through D refer tocorresponding optical transmitter chips 110A to 110D and opticalreceiver chips 120A to 120D and the understanding that the numbersuffixes -1 through -4 refer to corresponding inter-node waveguides130-1 to 130-4.

The optical transmitter chip 110A includes a plurality of opticaltransmitters 110A-1 to 110A-4. The optical transmitter chips 110B, 110C,and 110D similarly include a plurality of optical transmitters 110B-1 to110B-4, 110C-1 to 110C-4, and 110D-1 to 110D-4, respectively, but forease of illustration only the optical transmitters 110A-1 to 110A-4 areshown. Each of the optical transmitters 110A-1 to 110D-4 may be, forexample, a vertical-cavity surface-emitting laser (VCSEL), such thateach of the optical transmitter chips 110A to 110D may include a VCSELarray having VCSELs as the optical transmitters included therein. Theoptical signals emitted by the plurality of optical transmitters in oneof the optical transmitter chips 110A to 110D may be emitted at adifferent wavelength than the optical signals emitted by the pluralityof optical transmitters in another of the optical transmitter chips 110Ato 110D. Thus, the plurality of optical transmitters 110A-1 to 110D-4may include a first optical transmitter 110A-1 that emits an opticalsignal at a first wavelength and a second optical transmitter 110B-1that emits an optical signal at a second wavelength different from thefirst wavelength. The optical transmitter chips 110A to 110D may besemiconductor chips mounted on a board, e.g., a printed circuit board.In this way, a plurality of semiconductor chips mounted on a board mayinclude optical transmitter chips (e.g., optical transmitter chips 110Aand 110B), each of the optical transmitter chips including one or moreoptical transmitters (e.g., optical transmitter 110A-1 of opticaltransmitter chip 110A, optical transmitter 110B-1 of optical transmitterchip 110B), and the optical transmitter chips may include a firstoptical transmitter chip (e.g., optical transmitter chip 110A) whose oneor more optical transmitters emit optical signals at a first wavelengthand a second optical transmitter chip (e.g., optical transmitter chip110B) whose one or more optical transmitters emit optical signals at asecond wavelength different from the first wavelength.

The plurality of optical transmitters 110A-1 to 110D-4 may be dividedinto differential pairs in which one of the optical transmitters of adifferential pair emits a variable optical signal while the other of theoptical transmitters of the differential pair emits a reference opticalsignal. For example, the first and second optical transmitters (e.g.,optical transmitters 110A-1 and 110A-2) of each optical transmitter chip(e.g., optical transmitter chip 110A) may be a differential pairemitting a variable optical signal and a reference optical signal,respectively. In this way, each of the optical transmitter chips 110A to110D may include one or more differential pairs of optical transmitters.Similarly, the third and fourth optical transmitters (e.g., opticaltransmitters 110A-3 and 110A-4) of each optical transmitter chip (e.g.,optical transmitter chip 110A) may be a differential pair emitting avariable optical signal and a reference optical signal, respectively.Thus, each of the optical transmitter chips 110A to 110D may include twoor more differential pairs of optical transmitters. Among a differentialpair of optical transmitters 110A-1 and 110A-2 as an example, opticaltransmitter 110A-1 may emit a variable optical signal having a variablepower of “SigA1” and optical transmitter 110A-2 may emit a referenceoptical signal having a constant power of “RefA1,” so that thisdifferential pair can transmit a signal value corresponding todifferential power of SigA1-RefA1. Alternatively, among the differentialpair, optical transmitter 110A-1 may emit a variable optical signal“SigA1_positive” and optical transmitter 110A-2 may emit a variableoptical signal “SigA1_negative,” which is an inverted signal of“SigA1_positive.” In this implementation, the signal value can becalculated by ½ (SigA1_positive-SigA1_negative). As described in thisdisclosure, one of these signals (the positive or the negative) may bereferred to as “variable” while the other is referred to as “reference.”

The optical receiver chip 120A includes a plurality of optical receivers120A-1 to 120A-4. The optical receiver chips 120B, 120C, and 120Dsimilarly include a plurality of optical receivers 120B-1 to 120B-4,120C-1 to 120C-4, and 120D-1 to 120D-4, respectively, but for ease ofillustration only the optical receivers 120A-1 to 120A-4 are shown. Eachof the optical receivers 120A-1 to 120D-4 may be, for example, aphotodiode, such that each of the optical receiver chips 120A to 120Dmay include a photodiode array having photodiodes as the opticalreceivers included therein. The optical receiver chips 120A to 120D maybe semiconductor chips mounted on a board, e.g., a printed circuitboard. The board may be the same board on which the optical transmitterchips 110A to 110D are mounted. In this way, a plurality ofsemiconductor chips mounted on a board may include optical receiverchips (e.g., optical receiver chips 120A and 120B), each of the opticalreceiver chips including one or more optical receivers (e.g., opticalreceiver 120A-1 of optical receiver chip 120A, optical receiver 120B-1of optical receiver chip 120B). More generally, each of thesemiconductor chips mounted on the board may include at least one of theoptical transmitters (e.g., optical transmitter 110A-1) or at least oneof the optical receivers (e.g., optical receiver 120A-1).

The plurality of inter-node waveguides 130-1 to 130-4 are formed on aboard, e.g., a printed circuit board, and may be made of polymer in asingle layer of the board. (Note that “on” a board is not limited toformation in an upper layer of the board and includes formation insidethe board.) The plurality of inter-node waveguides 130-1 to 130-4 may beformed on the same board on which the optical transmitter chips 110A to110D and/or optical receiver chips 120A to 120D are mounted. Theplurality of inter-node waveguides 130-1 to 130-4 may be arranged asconcentric loops, e.g., circles, ovals, ellipses, rounded squares orrectangles, rounded pentagons, or any other rounded polygons or othershapes that can be arranged as concentric loops. In a case where theplurality of optical transmitters 110A-1 to 110D-4 includes a firstoptical transmitter 110A-1 that emits an optical signal at a firstwavelength and a second optical transmitter 110B-1 that emits an opticalsignal at a second wavelength different from the first wavelength, theinter-node waveguides 130-1 to 130-4 may include an inter-node waveguidethat propagates the optical signal at the first wavelength and theoptical signal at the second wavelength. All of the inter-nodewaveguides 130-1 to 130-4 may propagate optical signals at multiplewavelengths.

The plurality of multiplexers 140A to 140D are formed on a board, e.g.,a printed circuit board, each multiplexer 140A to 140D configured tomultiplex an input optical signal onto an inter-node waveguide of theplurality of inter-node waveguides 130-1 to 130-4. For example, themultiplexer 140A may be configured to multiplex input optical signalsonto each of the inter-node waveguides 130-1 to 130-4. Similarly, eachof the multiplexers 140B to 140D may be configured to multiplex inputoptical signals onto each of the inter-node waveguides 130-1 to 130-4.The plurality of multiplexers 140A to 140D may be formed on the sameboard on which the inter-node waveguides 130-1 to 130-4 are formedand/or the same board on which the optical transmitter chips 110A to110D and/or optical receiver chips 120A to 120D are mounted.

The plurality of transmitting waveguides 150A-1 to 150D-4 are formed ona board, e.g., a printed circuit board, such that at least one of thetransmitting waveguides 150A-1 to 150D-4 crosses at least one of theinter-node waveguides 130-1 to 130-4 with a core of one of the crossingwaveguides passing through a core or a clad of the other. The pluralityof transmitting waveguides 150A-1 to 150D-4 may be formed on the sameboard on which the inter-node waveguides 130-1 to 130-4 are formedand/or the same board on which the optical transmitter chips 110A to110D and/or optical receiver chips 120A to 120D are mounted. Thetransmitting waveguides 150A-1 to 150D-4 and inter-node waveguides 130-1to 130-4 may be made of polymer in a single layer of the board. Eachtransmitting waveguide 150A-1 to 150D-4 may be optically connected to anoptical transmitter of the plurality of optical transmitters 110A-1 to110D-4 and configured to receive an optical signal emitted from theoptical transmitter and transmit the received optical signal to aninter-node waveguide of the plurality of inter-node waveguides 130-1 to130-4 via a multiplexer of the plurality of multiplexers 140A to 140D.In the example shown in FIG. 1, the transmitting waveguide 150A-1(reference numeral omitted), which does not cross any of the inter-nodewaveguides 130-1 to 130-4, is optically connected to the opticaltransmitter 110A-1 (as schematically illustrated by its positioning) andconfigured to receive an optical signal emitted from the opticaltransmitter 110A-1 and transmit the received optical signal to theinter-node waveguide 130-1 via the multiplexer 140A. Similarly, thetransmitting waveguide 150A-2 (reference numeral omitted) is opticallyconnected to the optical transmitter 110A-2 and configured to receive anoptical signal emitted from the optical transmitter 110A-2 and transmitthe received optical signal to the inter-node waveguide 130-1 via themultiplexer 140A. However, unlike the transmitting waveguide 150A-1, thetransmitting waveguide 150A-2 crosses at least one of the inter-nodewaveguides 130-1 to 130-4, namely the inter-node waveguide 130-1. Byvirtue of the transparency of the transmitting waveguide 150A-2 and theinter-node waveguide 130-1, the core of the transmitting waveguide150A-2 may pass through the core or the clad of the inter-node waveguide130-1 on the way to the inter-node waveguide 130-2. Alternatively, thecore of the inter-node waveguide 130-1 may pass through the core or theclad of the transmitting waveguide 150A-2. To reduce cross talk ofoptical signals between crossing waveguides (e.g., part of an opticalsignal from one waveguide combining with an optical signal in the otherwaveguide), the angle between the crossing waveguides at the crossingpoint may be close to or substantially 90 degrees. Just as thetransmitting waveguides 150A-1 and 150A-2 are optically connected to andconfigured to receive optical signals emitted from respective opticaltransmitters 110A-1 and 110A-2 and transmit the received optical signalsto respective inter-node waveguides 130-1 and 130-2, the plurality oftransmitting waveguides 150A-1 to 150D-4 may be optically connected toand configured to receive optical signals emitted from respectiveoptical transmitters 110A-1 to 110D-4 and transmit the received opticalsignals to inter-node waveguides 130-1 to 130-4 with the understandingthat the letter suffixes A through D refer to corresponding opticaltransmitter chips 110A to 110D and the understanding that the numbersuffixes -1 through -4 refer to corresponding optical transmitters110A-1 to 110D4 and inter-node waveguides 130-1 to 130-4. The pluralityof mirrors 160A to 160D are formed on a board, e.g., a printed circuitboard, each mirror 160A to 160D arranged to partially reflect an opticalsignal propagating on an inter-node waveguide of the plurality ofinter-node waveguides 130-1 to 130-4 to produce a reflected opticalsignal. For example, the mirror 160A may partially reflect opticalsignals propagating on each of the inter-node waveguides 130-1 to 130-4.Similarly, each of the mirrors 160B to 160D may partially reflectoptical signals propagating on each of the inter-node waveguides 130-1to 130-4. As used throughout this disclosure, the term “mirror” mayrefer to a plurality of mirror elements arranged as a mirror array. Forexample, the mirror 160A may include a plurality of mirror elements thatseparately reflect the optical signals propagating on each of theinter-node waveguides 130-1, 130-2, 130-3, and 130-4 or a pluralitythereof. Also, the term “mirror” may refer to a single mirror element ofsuch a mirror array. The plurality of mirrors 160A to 160D may be formedon the same board on which the inter-node waveguides 130-1 to 130-4 areformed and/or the same board on which the optical transmitter chips 110Ato 110D and/or optical receiver chips 120A to 120D are mounted.

The plurality of receiving waveguides 170A-1 to 170D-4 are formed on aboard, e.g., a printed circuit board, such that at least one of thereceiving waveguides 170A-1 to 170D-4 crosses at least one of theinter-node waveguides 130-1 to 130-4 with a core of one of the crossingwaveguides passing through a core or a clad of the other. The pluralityof receiving waveguides 170A-1 to 170D-4 may be formed on the same boardon which the inter-node waveguides 130-1 to 130-4 are formed and/or thesame board on which the optical transmitter chips 110A to 110D and/oroptical receiver chips 120A to 120D are mounted. The receivingwaveguides 170A-1 to 170D-4, transmitting waveguides 150A-1 to 150D-4,and inter-node waveguides 130-1 to 130-4 may be made of polymer in asingle layer of the board. Each receiving waveguide 170A-1 to 170D-4 maybe optically connected to an optical receiver of the plurality ofoptical receivers 120A-1 to 120D-4 and configured to receive a reflectedoptical signal produced by a mirror of the plurality of mirrors 160A to160D and transmit the reflected optical signal to the optical receiver.In the example shown in FIG. 1, the receiving waveguide 170A-1(reference numeral omitted), which does not cross any of the inter-nodewaveguides 130-1 to 130-4, is optically connected to the opticalreceiver 120A-1 and configured to receive a reflected optical signalproduced by the mirror 160A and transmit the reflected optical signal tothe optical receiver 120A-1. Similarly, the receiving waveguide 170A-2(reference numeral omitted) is optically connected to the opticalreceiver 120A-2 and configured to receive a reflected optical signalproduced by the mirror 160A and transmit the reflected optical signal tothe optical receiver 120A-2. However, unlike the receiving waveguide170A-1, the receiving waveguide 170A-2 crosses at least one of theinter-node waveguides 130-1 to 130-4, namely the inter-node waveguide130-1. By virtue of the transparency of the receiving waveguide 170A-2and the inter-node waveguide 130-1, the core of the receiving waveguide170A-2 may pass through the core or the clad of the inter-node waveguide130-1 on the way to the optical receiver 120A-2. Alternatively, the coreof the inter-node waveguide 130-1 may pass through the core or the cladof the receiving waveguide 170A-2. To reduce cross talk of opticalsignals between crossing waveguides (e.g., part of an optical signalfrom one waveguide combining with an optical signal in the otherwaveguide), the angle between the crossing waveguides at the crossingpoint may be close to or substantially 90 degrees. Just as the receivingwaveguides 170A-1 and 170A-2 are optically connected to respectiveoptical receivers 120A-1 and 120A-2 and configured to receive reflectedoptical signals produced by the mirror 160A and transmit the reflectedoptical signals to the respective optical receivers 120A-1 and 120A-2,the plurality of transmitting waveguides 170A-1 to 170D-4 may beoptically connected to respective optical receivers 120A-1 to 120A-4 andconfigured to receive reflected optical signals produced by mirrors 160Ato 160D and transmit the reflected optical signal to the respectiveoptical receivers 120A-1 to 120D-4 with the understanding that theletter suffixes A through D refer to corresponding optical receiverchips 120A to 120D and the understanding that the number suffixes -1through -4 refer to corresponding optical receivers 120A-1 to 120D4.

The plurality of filters 180A to 180D are formed on a board, e.g., aprinted circuit board, each filter 180A to 180D configured to apply aweight to a reflected optical signal produced by a mirror of theplurality of mirrors 160A to 160D before the reflected optical signal istransmitted to an optical receiver 120A-1 to 120D-4 by the receivingwaveguide 170A-1 to 170D-4 that receives the reflected optical signal.For example, the filter 180A may be configured to apply weights toreflected optical signals produced by the mirror 160A before thereflected optical signals are transmitted to the optical receivers120A-1 to 120A-4 by the receiving waveguides 170A-1 to 170A-4.Similarly, each of the filters 180B to 180D may be configured to applyweights to reflected optical signals produced by the mirrors 180B to180D, respectively, before the reflected optical signals are transmittedto the optical receivers 120B-1 to 120B-4, 120C-1 to 120C-4, and 120D-1to 120D-4, respectively. The plurality of filters 180A to 180D may beformed on the same board on which the inter-node waveguides 130-1 to130-4 are formed and/or the same board on which the optical transmitterchips 110A to 110D and/or optical receiver chips 120A to 120D aremounted. As used throughout this disclosure, the term “filter” may referto a plurality of filter elements arranged as a filter array. Forexample, the filter 180A may include a plurality of filter elements thatapply separate weights to optical signals transmitted on each of thereceiving waveguides 170A-1, 170A-2, 170A-3, and 170A-4. Similarly, thefilter 180B may include a plurality of filter elements that applyseparate weights to optical signals transmitted one each of thereceiving waveguides 170B-1, 170B-4, 170B-3, and 170B-4.

Each of intra-node signal lines 190A-1 to 190D-4 is connected to anoptical receiver of the plurality of optical receivers 120A-1 to 120D-4and an optical transmitter of the plurality of optical transmitters110A-1 to 110D-4 and is configured to receive an electrical signalrepresenting a power of an optical signal received by the opticalreceiver and transmit the electrical signal to the optical transmitter,thereby connecting the optical receiver and the optical transmitter toform an input and an output of a neuron. For example, the intra-nodesignal 190A-1 may be connected to the optical receiver 120A-1 and theoptical transmitter 110A-1 and configured to receive an electricalsignal representing a power of an optical signal received by the opticalreceiver 120A-1 and transmit the electrical signal to the opticaltransmitter 110A-1, thereby connecting the optical receiver 120A-1 andthe optical transmitter 110A-1 to form an input and an output of aneuron. (The various waveguides, including the transmitting waveguides,receiving waveguides, and inter-node waveguides, may thus function assynapses.) In this way, in the specific example illustrated in FIG. 1,each set of transmitter chips 110 and receiver chips 120 having the sameletter suffix (e.g., transmitter chip 110A and receiver chip 120A) maycomprise two or four neurons depending on whether the opticaltransmitters 110A-1 to 110D-4 are divided into differential pairs. Inthe case of differential pairs, for example, the set of transmitter chip110A and receiver chip 120A may include a first neuron having a variableoptical transmitter 110A-1, a reference optical transmitter 110A-2,optical receivers 120A-1 and 120A-2, and intra-node signal lines 190A-1and 190A-2 and may include a second neuron having a variable opticaltransmitter 110A-3, a reference optical transmitter 110A-4, opticalreceivers 120A-3 and 120A-4, and intra-node signal lines 190A-3 and190A-4. However, the number of neurons in a chip pair can be any number.Furthermore, in some embodiments, optical transmitters and opticalreceivers can be implemented in a single chip.

In FIG. 1, each of the optical transmitter chips 110A to 110D includesthe same number of optical transmitters (e.g., four optical transmitters110A-1 to 110A-4 for optical transmitter chip 110A) and each of theoptical receiver chips 120A to 120D includes the same number of opticalreceivers (e.g., four optical receivers 120A-1 to 120A-4 for opticalreceiver chip 120A). Moreover, the number of optical transmitters (e.g.,four) included in each of the optical transmitter chips 110A to 110D isthe same as the number of optical receivers (e.g., four) included ineach of the optical receiver chips 120A to 120D. In this case, thenumber of inter-node waveguides 130-1 to 130-4 connected to each of theoptical transmitter chips via the transmitting waveguides (e.g., four,such as inter-node waveguides 130-1 to 130-4 connected to opticaltransmitter chip 110A via transmitting waveguides 150A-1 to 150A-4, orinter-node waveguides 130-1 to 130-4 connected to optical transmitterchip 110B via transmitting waveguides 150A-1 to 150A-4) may be the sameas the number of optical transmitters included in each of the opticaltransmitter chips (e.g., four) and the number of optical receiversincluded in each of the optical receiver chips (e.g., four). By matchingthe number of inter-node waveguides 130-1 to 130-4 to the numbers ofoptical transmitters/receivers per chip, each of the inter-nodewaveguides 130-1 to 130-4 can be dedicated to the same-positionedoptical transmitter/receiver of each chip to define a channel, e.g.,channels corresponding to the number suffixes -1 to -4. Thus, forexample, if the second optical transmitter (e.g., optical transmitter110A-2 or 110B-2) of each optical transmitter chip (e.g., opticaltransmitter chip 110A or 110B) emits a reference optical signal of adifferential signal as described above, all of the second opticaltransmitters (e.g., optical transmitters 110A-2, 110B-2, 110A-3, and110A-2), all of the second optical receivers (e.g., optical receivers120A-2, 120B-2, 120C-2, and 120D-2), all of the second transmittingwaveguides (e.g., transmitting waveguides 150A-2, 150B-2, 150C-2, and150D-2), all of the second receiving waveguides (e.g., receivingwaveguides 170A-2, 170B-2, 170C-2, and 170D-2), and theinternode-waveguide 130-2 may define a reference channel for use by aplurality of differential pairs of optical transmitters.

FIG. 2 shows an example diagram of a region of the waveguidearchitecture shown in FIG. 1, namely the region indicated by the dashedcircle in FIG. 1. As shown in FIG. 2, the multiplexer 140A includes anentrance mirror 141A and a y-shaped waveguide structure 142A-1 connectedby a first entrance arm and an exit arm to an inter-node waveguide 130-1onto which the multiplexer 140A multiplexes its input signal, theentrance mirror 141A configured to receive, as the input signal, anoptical signal transmitted by a transmitting waveguide 150A-1 of theplurality of waveguides and reflect the input signal to produce areflected optical signal that enters a second entrance arm of they-shaped waveguide structure and joins an optical signal propagating onthe inter-node waveguide 130-1 where the second entrance arm meets thefirst entrance arm of the y-shaped waveguide structure 142A-1. The firstentrance arm and the exit arm of the y-shaped waveguide structure 142A-1may physically be lengths of the inter-node waveguide 130-1, e.g., thoselengths before and after the point where the second entrance arm meetsthe inter-node waveguide 130-1 to form the y-shaped waveguide structure142A-1. For this reason, only the second entrance arm of the y-shapedwaveguide structure 142A-1 is shown as a separate structure from theinter-node waveguide 130-1 in FIG. 2. The entrance mirror 141A may havea reflection coefficient of substantially 1 for light incident on theside facing the transmitting waveguide 150A-1 while having a reflectioncoefficient of substantially 0 for light incident on the opposite side.In this way, the entrance mirror 141A may reflect the optical signaltransmitted by the transmitting waveguide 150A-1 so that the reflectedoptical signal enters the second entrance arm of the y-shaped waveguidestructure 142-1 while allowing optical signals propagating on theinter-node waveguide 130-1 to pass through so as to enter the firstentrance arm of the y-shaped waveguide structure 142-1.

The y-shaped waveguide structures 142-2 to 142-4 may have the samefunctionality with respect to the transmitting waveguides 150-2 to 152-4and inter-node waveguides 130-2 to 130-4 as the y-shaped waveguidestructure 142-1 has with respect to the transmitting waveguide 150-1 andinter-node waveguide 130-1. The multiplexer 140A may refer to thecombination of the entrance mirror 141A and each of the y-shapedwaveguide structures 142A-1 to 142-4. Alternatively, the multiplexer140A may refer to the entrance mirror 141A in combination with a singley-shaped waveguide structure (e.g., 142A-1), such that FIG. 2 shows fourmultiplexers 140A that share the entrance mirror 141A.

FIG. 3 shows an example diagram of the waveguide architecture shown inFIG. 1 including reflection coefficients of the mirrors 160A to 160D.Due to limited space, only the optical transmitter chips 110A to 110D,optical receiver chips 120A to 120D, inter-node waveguides 130-1 to130-4, and mirrors 160A to 160D are given reference numbers in FIG. 3and none of the individual optical transmitters 110A-1 to 110D-4 oroptical receivers 120A-1 to 110D-4 are shown. Furthermore, the labels“Tx” and “Rx” for the optical transmitter chips 110A to 110D and opticalreceiver chips 120A to 120D have been omitted, and in their place eachof the optical transmitter chips 110A to 110D is labeled by acorresponding wavelength λA to λD. As indicated by these labels, in theexample shown in FIG. 3, the optical transmitter chips 110A to 110D arededicated to corresponding transmission wavelengths λA to λD,respectively. That is, the optical signals emitted by the plurality ofoptical transmitter chips 110A-1 to 110A-4 of optical transmitter chip110A are at the wavelength λA, the optical signals emitted by theplurality of optical transmitter chips 110B-1 to 110B-4 of opticaltransmitter chip 110B are at the wavelength λB, etc. Thus, for example,the optical signals emitted by optical transmitters 110A-1, 110B-1,110C-1, and 110D-1 are at respective wavelengths λA, λB, λC, and λD, andthese four optical signals of different wavelengths are respectivelytransmitted by transmitting waveguides 150A-1, 150B-1, 150C-1, and150D-1 and multiplexed onto the inner-most inter-node waveguide 130-1 byrespective multiplexers 140A, 140B, 140C, and 140D using, e.g.,wavelength division multiplexing (WDM). Similarly, the optical signalsemitted by optical transmitters 110A-2, 110B-2, 110C-2, and 110D-2 areat respective wavelengths λA, λB, λC, and λD, and these four opticalsignals of different wavelengths may be respectively transmitted bytransmitting waveguides 150A-2, 150B-2, 150C-2, and 150D-2 andmultiplexed onto the next inter-node waveguide 130-2 by respectivemultiplexers 140A, 140B, 140C, and 140D using, e.g., wavelength divisionmultiplexing (WDM). The third and fourth channels may functioncorrespondingly. Thus, optical signals of four wavelengths λA, λB, λC,and λD may propagate on each of the four inter-node waveguides 130-1 to130-4.

In the example shown in FIG. 3, the mirrors 160A to 160D are configuredsuch that the optical receiver chips 120A to 120D of each chip pair(each pair of optical receiver chip and optical transmitting chip)receives all of the optical signals emitted by the optical transmitterchips of the other chip pairs. For example, the mirror 160A isconfigured such that the optical receiver chip 120A receives all of theoptical signals emitted by the optical transmitter chips 120B, 120C, and120D. Specifically, as shown by way of example in FIG. 3, the reflectioncoefficient of the mirror 160A may depend on wavelength. For example, abragg filter or combination of bragg filters having differenttransparencies for different wavelengths may be used as any of themirrors 160A to 160D. With the waveguide architecture shown in FIG. 3,the optical signals propagating on the inter-node waveguides 130-1 to130-4 are traveling counterclockwise. Thus, when the optical signalsemitted by the optical transmitter chip 110D reach the mirror 160A to bereflected to the optical receiver chip 120A, the optical signals haveyet to arrive at mirrors 160B and 160C to be reflected to the opticalreceiver chips 120B and 120C and must be allowed to transmit through themirror 160A accordingly. When the optical signals emitted by the opticaltransmitter chip 110C arrive at the optical receiver 120A, the opticalsignals have yet to arrive at mirror 160B and must be allowed totransmit through the mirror 160A accordingly. When the optical signalsemitted by the optical transmitter chip 110C arrive at the opticalreceiver 120A, the optical signals do not need to go further (in thecase where they do not need to be received by the optical receiver chip110C of the same chip pair as the optical transmitter chip 110C).

On the basis of these principles, the mirrors 160A to 160D may beconfigured as shown in FIG. 3, such that (using mirror 160A as arepresentative example) the reflection coefficient for the wavelength λDis about 0.33 or one-third, allowing for the optical signal emitted fromthe optical transmitter chip 110D to still be received by two opticalreceiver chips 120B and 120C, the reflection coefficient for thewavelength λC is about 0.5, allowing for one-half of the remainingtwo-thirds of the optical signal emitted from the optical transmitterchip 110C to still be received by one optical receiver chip 120B (thefirst one-third having been reflected by the mirror 160D), and thereflection coefficient for the wavelength λB is about 1, e.g., theremainder of the optical signal emitted from the optical transmitterchip 110C (after the first two-thirds have been reflected by the mirrors160C and 160D). As for the reflection coefficient for the wavelength λA,it is indicated in FIG. 3 as 0* because it may be zero in someembodiments, allowing for no reflection by the mirror 160A of theremaining optical signal emitted from the optical transmitter chip 110A,or it may be any arbitrary value under the assumption that no such λAoptical signal remains after having been reflected by the mirrors 160B,160C, an 160D. The mirrors 160B, 160C, and 160D may be configuredcorrespondingly, as shown in FIG. 3. Thus, for each of the opticalreceivers 120A-1 to 120D-4 that is connected to an optical transmitter110A-1 to 110D-4 via an intra-node signal line 190A-1 to 190D-4, theplurality of mirrors 160A to 160D includes a mirror whose reflectedoptical signal is transmitted to the optical receiver and whosereflection coefficient is substantially zero for a wavelength of theoptical signal emitted by the optical transmitter. With these reflectioncoefficients λA to λD, each optical signal from each optical transmittermay be substantially reflected and divided into a plurality of opticalsignals having substantially the same power (e.g., ⅓ of the transmittedoptical signal in this embodiment without considering optical lossthrough waveguides) and each divided optical signal may be propagatedthrough a corresponding receiving waveguide.

FIG. 4 shows an example diagram of the region of the waveguidearchitecture shown in FIG. 2 including arbitrary weights of the filter180A. Due to limited space and for simplicity, only the inter-nodewaveguides 130-1 to 130-4, transmitting waveguides 150A-1 to 150A-4,mirror 160A, receiving waveguides 170A-1 to 170A-4, and filter 180A aregiven reference numbers in FIG. 4. In the example of FIG. 4, the filter180A is a spectral filter whose applied weight depends on wavelength.The example of FIG. 4 uses the same convention regarding wavelengths asFIG. 3. That is, the wavelengths λA, λB, λC, and λD are the wavelengthsof the optical signals emitted by the optical transmitter chips 110A,110B, 110C, and 110D, respectively. As further described by way ofexample with respect to FIG. 3, such optical signals of four wavelengthsmay propagate on each of the inter-node waveguides 130-1, 130-2, 130-3,and 130-4 and may be reflected by the mirror 160A such that reflectedoptical signals of each of the four wavelengths (or three out of four,depending on the configuration of the mirrors 160A to 160D) istransmitted by each receiving waveguide 170A-1, 170A-2, 170A-3, and170A-4 to the optical receiver chip 120A. By using a spectral filter asthe filter 180A, the optical signal of each wavelength may be weighteddifferently. It should also be noted that the weighting scheme may bedifferent for each of the receiving waveguides 170A-1, 170A-2, 170A-3,and 170A-4, since the filter may be a filter array including multiplefilter elements as described above.

In the specific example shown in FIG. 4, arbitrary weights are depictedfor each wavelength for each of the receiving waveguides 170A-1, 170A-2,170A-3, and 170A-4. For simplicity, three shades are used: whiterepresenting relatively “transparent” filtering, e.g., a high weight,black representing relatively “opaque” filtering, e.g., a low weight,and gray representing filtering with a mid-level weight. However, anynumber of weight gradations may be possible. In the example of FIG. 4,the second and fourth channels, e.g., the channels including receivingwaveguides 170A-2 and 170A-4 are for reference optical signals ofdifferential pairs, and thus they are given the mid-level weight (gray)for all wavelengths in this example. The weights depicted for the firstand third channels, e.g., the channels including receiving waveguides170A-1 and 170A-3, are intended to represent any arbitrary distributionof weights. In this way, the filter 180A may separately weight theoptical signals emitted by each of the optical transmitters 110A-1 to110D-4. Similarly, the filters 180B, 180C, and 180D may separatelyweight the optical signals emitted by each of the optical transmitters110A-1 to 110D-4, either by using identical or different weightdistributions. In some embodiments, the filter 180A need not apply anyweight (or may apply a zero weight) to optical signals having thewavelength λA because the mirrors 160A to 160D may be configured toprevent the receiving waveguides 170A-1 to 170A-4 from receiving opticalsignals having the wavelength λA (such optical signals having beenemitted by the optical transmitter chip 110A of the same chip pair). Thesame may be correspondingly true for the other filters 180B to 180D.

In some embodiments, it may be possible to change the weights of thefilters 180A to 180D. For example, the filters 180A to 180D may includeone or more exchangeable filters that can be exchanged, e.g., physicallyremoved and replaced, to change the applied weight(s). This replacementcan be done by manual operation of a user. Instead, a manipulator or amechanism controlled by a controller or a computer connected to orincluded in the photonic neural component 100 may change each filter180A to 180D or the individual filter elements on each receivingwaveguide 170A-1 to 170D-4. As another example, the filters 180A to 180Dmay include one or more variable filters whose transparency can bevaried to change the applied weights(s). Varying the transparency may beaccomplished in various ways, e.g., using liquid crystal filters whosetransparency can be changed by changing the driving voltage, usingoptical attenuators to change the power of the light, dividing anoptical signal into several sub-waveguides and selectively turning ONand OFF optical switches to allow only a portion of the sub-waveguidesto propagate the optical signal. Such configurations for varying of thetransparency to adjust the weight may be employed after splitting theoptical signals on each of the receiving waveguides 170A-1 to 170A-4into the respective wavelengths λA, λB, λC, and λD. As a result, opticalreceiver 120D-1, as an example, may receive optical signals having atotal power of P_(RxD-1)=⅓ (W_(λAD-1) T_(TxA-1)+W_(λBD-1)T_(TxB-1)+W_(λCD-1) T_(TxC-1)) without considering power loss throughwaveguides, where T_(TxA-1), T_(TxB-1), and T_(TxC-1) represent powersof the emitted optical signals from optical transmitters 110A-1, 110B-1,and 110C-1 respectively, W_(λAD-1), W_(λBD-1), and W_(λCD-1) are weightsbased on the transparency coefficients of filter 180A for receivingwaveguide 170D-1 at wavelengths λA, λB, and λC respectively, adifferential pair of optical receiver 120D-1 and 120D-2 receivedifferential optical signals having powers of P_(RxD-1) and P_(RxD-2),and a received value is calculated based on the difference of thesepowers (e.g., P_(RxD1&2)=P_(RxD-1)−P_(RxD-2)). A set of a differentialpair of optical receivers (e.g., 120D-1 and 120D-2) and a correspondingdifferential pair of optical transmitters (e.g., 110D-1 and 110D-2) maybe included in each neuron, and the output of the neuron may becalculated by applying a neural output function f(x) such as a sigmoidfunction to a received value or an Integrate and Fire spiking model. Forexample, the value of the output signal, represented by the differenceof optical powers output from the differential pair of opticaltransmitters 110D-1 and 110D-2, may be determined (e.g., proportionallydetermined) based on f(P_(RxD1&2)).

FIG. 5 shows an example diagram side view of a portion of a board onwhich the transmitter chip 110A and the transmitting waveguide 150A-1are formed. In the example shown in FIG. 5, the board on which thetransmitting waveguide 150A-1 is formed is the same board on which theoptical transmitter chip 110A is mounted. As shown in FIG. 5, thetransmitting waveguide 150A-1 is formed on a surface of the board(represented by the horizontal surface on which the transmittingwaveguide 150A-1 is formed), along with an entrance mirror 510configured to redirect light from a direction perpendicular to the boardto a direction parallel to the board, e.g., at a substantially 45° anglewith respect to the board. The optical transmitter chip 110A, includingthe optical transmitter 110A-1, is mounted on the board with the opticaltransmitter 110A-1 facing the board, e.g., by flip chip bonding. Thedashed line schematically represents an optical signal emitted by theoptical transmitter 110A-1.

FIG. 6 shows an example diagram side view of a portion of a board onwhich the receiver chip 120A and the receiving waveguide 170A-1 areformed. In the example of FIG. 6, the board on which the receivingwaveguide 170A-1 is formed is the same board on which the opticalreceiver chip 170A is mounted. As shown in FIG. 6, the receivingwaveguide 170A-1 is formed on a surface of the board (represented by thehorizontal surface on which the transmitting waveguide 170A-1 isformed), along with an exit mirror 610 configured to redirect light froma direction parallel to the board to a direction perpendicular to theboard, e.g., at a substantially 45° angle with respect to the board. Theoptical receiver chip 120A, including the optical receiver 120A-1, ismounted on the board with the optical receiver 120A-1 facing the board,e.g., by flip chip bonding. The dashed line schematically represents anoptical signal received by the optical receiver 120A-1.

The configuration described with respect to FIG. 5 may also apply to theremainder of the transmitting waveguides 150A-2 to 150A-4 connected tothe optical transmitter chip 110A, and the configuration described withrespect to FIG. 6 may also apply to the remainder of the receivingwaveguides 170A-2 to 170A-4 connected to the optical receiver chip 120A.Moreover, the configurations described with respect to FIGS. 5 and 6 mayapply correspondingly to the transmitting waveguides 150B-1 to 150D-4and optical transmitter chips 110B to 110D and to the receivingwaveguides 170B-1 to 170D-4 and optical receiver chips 120B to 120D.Thus, each of the optical transmitter chips 110A to 110D and opticalreceiver chips 120A to 120D may be arranged such that at least oneoptical transmitter included in the chip (e.g., optical transmitter110A-1) or at least one optical receiver included in the chip (e.g.,optical receiver 120A-1) faces the board, with the transmittingwaveguides 150A-1 to 150D-4 connected to the optical transmitters 110A-1to 110D-4 via the entry mirrors 510 and the receiving waveguides 170A-1to 170D-4 connected to the optical receivers 120A-1 to 120D-4 via theexit mirrors 610.

The various waveguides and the multiplexers 140A to 140D of the photonicneural component 100 may be manufactured by forming a lower clad layerin a layer of a board, forming a core layer on the lower clad layer, andforming an upper clad layer on the core layer. The lower and upper cladlayers may be formed, for example, by applying a first polymer usingspin coating or curtain coating and baking. The lower and upper cladlayers may be shared by multiple parallel waveguides. The core layer maybe formed, for example, by applying a second or the same polymer usingspin coating or curtain coating and baking, wherein a photomask patternhaving an opening in a portion to be the core is formed on the secondpolymer and irradiated with ultraviolet rays to increase the refractiveindex. The mirrors 160A to 160D, entry mirrors 510, and exit mirrors560, may be formed during the formation of the waveguides, e.g., bycutting an end portion of the core and forming a reflective surface byvapor deposition of mirror material such as aluminum, silver, etc. or atotal internal reflection mechanism may be used.

FIG. 7 shows an example diagram of a waveguide architecture for aphotonic neural component 100 according to an embodiment of theinvention. The architecture of FIG. 7 is an example of how thearchitecture of FIG. 1 may be expanded to include more pairs oftransmitter and receiver chips, e.g., more neurons. Due to limitedspace, out of the plurality of transmitting waveguides 150B-1 to 150B-4,150D-1 to 150D-4, 150E-5 to 150E-8, 150E-5 to 150E-8, and 150H-5 to150H-8, only transmitting waveguides 150D-1 to 150D-4 are givenreference numbers in FIG. 7. Similarly, out of the plurality ofmultiplexers 140A to 140H only multiplexer 140B is given a referencenumber in FIG. 7, out of the plurality of mirrors 160A to 160H onlymirror 160B is given a reference number in FIG. 7, out of the pluralityof filters 180B, 180D, 180E, 180F, and 180H only filter 180B is given areference number in FIG. 7, out of the plurality of receiving waveguides170B-1 to 170B-4, 170D-1 to 170D-4, 170E-5 to 170E-8, 170E-5 to 170E-8,and 170H-5 to 170H-8 only receiving waveguides 170D-1 to 170D-4 aregiven reference numbers in FIG. 7, and out of the plurality ofintra-node signal lines 190B-1 to 190B-4, 190D-1 to 190D-4, 190E-5 to190E-8, 190E-5 to 190E-8, and 190H-5 to 190H-8 only intra-node signallines 190H-5 to 190H-8 are given reference numbers in FIG. 7.Nevertheless, the omitted reference numbers of transmitting waveguides,multiplexers, mirrors, receiving waveguides, filters, and intra-nodesignal lines depicted in FIG. 7 may be referred to throughout thisdisclosure with the understanding that the letter suffixes A through Hrefer to corresponding optical transmitter chips 110A to 110H andoptical receiver chips 120H to 120H and the understanding that thenumber suffixes -1 through -8 refer to corresponding inter-nodewaveguides 130-1 to 130-8.

Just as the optical transmitter chips 110A to 110D of FIG. 1 includerespective pluralities of optical transmitters 110A-1 to 110A-4, 110B-1to 110B-4, 110C-1 to 110C-4, and 110D-1 to 110D-4, the opticaltransmitter chips 110A to 110H of FIG. 7 include respective pluralitiesof optical transmitters 110A-1 to 110A-4, 110B-1 to 110B-4, 110C-1 to110C-4, 110D-1 to 110D-4, 110E-5 to 110E-8, 110E-5 to 110E-8, 110G-5 to110G-8, and 110H-5 to 110H-8, but for ease of illustration none of theoptical transmitters are shown in FIG. 7. In the same way, just as theoptical receiver chips 120A to 120D of FIG. 1 include respectivepluralities of optical receivers 120A-1 to 120A-4, 120B-1 to 120B-4,120C-1 to 120C-4, and 120D-1 to 120D-4, the optical receiver chips 120Ato 120H of FIG. 7 include respective pluralities of optical receivers120A-1 to 120A-4, 120B-1 to 120B-4, 120C-1 to 120C-4, 120D-1 to 120D-4,120E-5 to 110E-8, 120E-5 to 120E-8, 120G-5 to 120G-8, and 120H-5 to120H-8, but for ease of illustration none of the optical receivers areshown in FIG. 7.

In the example of FIG. 1, the plurality of inter-node waveguides 130-1to 130-4 includes a first ring (e.g., inter-node waveguides 130-1 to130-4) having two or more of the inter-node waveguides arranged asconcentric loops, the plurality of optical transmitters 110A-1 to 110D-4includes a first inner optical transmitter group (e.g., opticaltransmitters 110A-1 to 110D-4) having two or more of the opticaltransmitters disposed inside the first ring, and the plurality ofoptical receivers 120A-1 to 120D-4 includes a first inner opticalreceiver group (e.g., optical receivers 120A-1 to 120D-4) having two ormore of the optical receivers disposed inside the first ring. In theexample of FIG. 7, similarly to FIG. 1, the plurality of inter-nodewaveguides 130-1 to 130-8 includes a first ring (e.g., inter-nodewaveguides 130-1 to 130-4) having two or more of the inter-nodewaveguides arranged as concentric loops, the plurality of opticaltransmitters 110A-1 to 110A-4, 110B-1 to 110B-4, 110C-1 to 110C-4,110D-1 to 110D-4, 110E-5 to 110E-8, 110E-5 to 110E-8, 110G-5 to 110G-8,and 110H-5 to 110H-8 includes a first inner optical transmitter group(e.g., optical transmitters 110B-1 to 110B-4 and 110D-1 to 110D-4)having two or more of the optical transmitters disposed inside the firstring, and the plurality of optical receivers 120A-1 to 120A-4, 120B-1 to120B-4, 120C-1 to 120C-4, 120D-1 to 120D-4, 120E-5 to 110E-8, 120E-5 to120E-8, 120G-5 to 120G-8, and 120H-5 to 120H-8 includes a first inneroptical receiver group (e.g., optical receivers 120B-1 to 120B-4 and120D-1 to 120D-4) having two or more of the optical receivers disposedinside the first ring. The plurality of optical transmitters 110A-1 to110A-4, 110B-1 to 110B-4, 110C-1 to 110C-4, 110D-1 to 110D-4, 110E-5 to110E-8, 110E-5 to 110E-8, 110G-5 to 110G-8, and 110H-5 to 110H-8 mayfurther include a first outer optical transmitter group (e.g., opticaltransmitters 110A-1 to 110A-4 and 110C-1 to 110C-4) having two or moreof the optical transmitters disposed outside the first ring, and theplurality of optical receivers 120A-1 to 120A-4, 120B-1 to 120B-4,120C-1 to 120C-4, 120D-1 to 120D-4, 120E-5 to 110E-8, 120E-5 to 120E-8,120G-5 to 120G-8, and 120H-5 to 120H-8 may further include a first outeroptical receiver group (e.g., optical receivers 120A-1 to 120A-4 and120C-1 to 120C-4) having two or more of the optical receivers disposedoutside the first ring.

As shown in FIG, 7, the plurality of inter-node waveguides 130-1 to130-8 may further include a second ring (e.g., inter-node waveguides130-5 to 130-8) having two or more of the inter-node waveguides arrangedas concentric loops, the plurality of optical transmitters 110A-1 to110A-4, 110B-1 to 110B-4, 110C-1 to 110C-4, 110D-1 to 110D-4, 110E-5 to110E-8, 110E-5 to 110E-8, 110G-5 to 110G-8, and 110H-5 to 110H-8includes a second inner optical transmitter group (e.g., 110E-5 to110E-8, 110E-5 to 110E-8, and 110H-5, to 110H-8) having two or more ofthe optical transmitters disposed inside the second ring, and theplurality of optical receivers 120A-1 to 120A-4, 120B-1 to 120B-4,120C-1 to 120C-4, 120D-1 to 120D-4, 120E-5 to 120E-8, 120E-5 to 120E-8,120G-5 to 120G-8, and 120H-5 to 120H-8 includes a second inner opticalreceiver group (e.g., 120E-5 to 120E-8, 120E-5 to 120E-8, and 120H-5, to120H-8) having two or more of the optical receivers disposed inside thesecond ring. The plurality of optical transmitters 110A-1 to 110A-4,110B-1 to 110B-4, 110C-1 to 110C-4, 110D-1 to 110D-4, 110E-5 to 110E-8,110E-5 to 110E-8, 110G-5 to 110G-8, and 110H-5 to 110H-8 may furtherinclude a second outer optical transmitter group (e.g., opticaltransmitters 110G-5 to 110G-8) having two or more of the opticaltransmitters disposed outside the second ring, and the plurality ofoptical receivers 120A-1 to 120A-4, 120B-1 to 120B-4, 120C-1 to 120C-4,120D-1 to 120D-4, 120E-5 to 110E-8, 120E-5 to 120E-8, 120G-5 to 120G-8,and 120H-5 to 120H-8 may further include a second outer optical receivergroup (e.g., optical receivers 120G-5 to 120G-8) having two or more ofthe optical receivers disposed outside the second ring.

As described above, the plurality of inter-node waveguides 130-1 to130-8 may be divided into multiple rings (e.g., the first ring includinginter-node waveguides 130-1 to 130-4 and the second ring includinginter-node waveguides 130-5 to 130-8), while the optical transmittersand optical receivers (and equally the optical transmitter chips andoptical receiver chips) can be divided into inner and outer groupsassociated with each ring. In the same way, the plurality ofmultiplexers 140A to 140H may include a first multiplexer group (e.g.,multiplexers 140A to 140D), each multiplexer of the first multiplexergroup configured to multiplex an input optical signal onto an inter-nodewaveguide of the first ring (e.g., inter-node waveguides 130-1 to130-4), and a second multiplexer group (e.g., multiplexers 140E to140H), each multiplexer of the second multiplexer group configured tomultiplex an input optical signal onto an inter-node waveguide of thesecond ring (e.g., inter-node waveguides 130-5 to 130-8). Likewise, theplurality of mirrors 160A to 160H may include a first mirror group(e.g., mirrors 160A to 160D), each mirror of the first mirror groupconfigured to partially reflect an optical signal propagating on aninter-node waveguide of the first ring (e.g., inter-node waveguides130-1 to 130-4) to produce a reflected optical signal, and a secondmirror group (e.g., mirrors 160E to 160H), each mirror of the secondmirror group configured to partially reflect an optical signalpropagating on an inter-node waveguide of the second ring (e.g.,inter-node waveguides 130-5 to 130-8) to produce a reflected opticalsignal. The filters 180B, 180D, 180E, 180F, and 180H and the intra-nodesignal lines 190B-1 to 190B-4, 190D-1 to 190D-4, 190E-5 to 190E-8,190E-5 to 190E-8, and 190H-5 to 190H-8 may similarly be divided intogroups associated with each ring.

In place of receiving waveguides 170A-1 to 170A-4, 170C-1 to 170C-4, and170G-5 to 170G-8, the waveguide architecture of FIG. 7 instead includesoutput waveguides 710A-1 to 710A-4, 710C-1 to 710C-4, and 710G-5 to710G-8, divided into first output waveguides 710A-1 to 710A-4 and 710C-1to 710C-4 associated with the first ring and second output waveguides710G-5 to 710G-8 associated with the second ring. (Due to limited space,only output waveguides 710C-1 to 710C-4 are given reference numbers inFIG. 7.) The first output waveguides 710A-1 to 710A-4 and 710C-1 to710C-4 may be formed on the board such that at least one of the firstoutput waveguides (e.g., first output waveguide 710C-3) crosses at leastone of the inter-node waveguides of the first ring (e.g., inter-nodewaveguide 130-4) with a core of one of the crossing waveguides passingthrough a core or a clad of the other. Each first output waveguide(e.g., 710C-3) may be connected to outside the first ring and configuredto receive a reflected optical signal produced by a mirror of the firstmirror group (e.g., mirror 160C) and transmit the reflected opticalsignal to outside the first ring. Similarly, the second outputwaveguides 710G-5 to 710G-8 may be formed on the board such that atleast one of the second output waveguides (e.g., second output waveguide710G-7) crosses at least one of the inter-node waveguides of the secondring (e.g., inter-node waveguide 130-8) with a core of one of thecrossing waveguides passing through a core or a clad of the other. Eachsecond output waveguide (e.g., 710G-7) may be connected to outside thesecond ring and configured to receive a reflected optical signalproduced by a mirror of the second mirror group (e.g., mirror 160G) andtransmit the reflected optical signal to outside the second ring.

In place of filters 180A, 180C, and 180G, the waveguide architecture ofFIG. 7 instead includes output filters 720A, 720C, and 720G, dividedinto first output filters 720A and 720C associated with the first ringand a second output waveguide 720G associated with the second ring. Thefirst output filter 720A is formed on the board and configured to applya weight to a reflected optical signal produced by a mirror 160A of theplurality of mirrors before the reflected optical signal is transmittedto outside the first ring by the first output waveguide (e.g., firstoutput waveguide 710A-1, 710A-2, 710A-3, or 710A-4) that receives thereflected optical signal. Similarly, the first output filter 720C isformed on the board and configured to apply a weight to a reflectedoptical signal produced by a mirror 160C of the plurality of mirrorsbefore the reflected optical signal is transmitted to outside the firstring by the first output waveguide (e.g., first output waveguide 710C-1,710C-2, 710C-3, or 710C-4) that receives the reflected optical signal.Correspondingly, the second output filter 720G is formed on the boardand configured to apply a weight to a reflected optical signal producedby a mirror 160G of the plurality of mirrors before the reflectedoptical signal is transmitted to outside the second ring by the firstoutput waveguide (e.g., first output waveguide 710G-5, 710G-6, 710G-7,or 710G-8) that receives the reflected optical signal.

Each of the optical receivers of the first outer optical receiver group(e.g., optical receivers 120A-1 to 120A-4 and 120C-1 to 120C-4) may beoptically connected to a first output waveguide of the plurality offirst output waveguides (e.g., 710A-1 to 710A-4 and 710C-1 to 710C-4)and configured to receive the reflected optical signal transmitted bythe first output waveguide. Similarly, each of the optical receivers ofthe second outer optical receiver group (e.g., optical receivers 120G-5to 120G-8) may be optically connected to a second output waveguide ofthe plurality of second output waveguides (e.g., second outputwaveguides 710G-5 to 710G-8) and configured to receive the reflectedoptical signal transmitted by the second output waveguide. That is, eachsecond output waveguide (e.g., second output waveguide 710G-5, 710G-6,710G-7, or 710G-8) may be optically connected to an optical receiver ofthe second outer optical receiver group (e.g., optical receiver 120G-5,120G-6, 120G-7, or 120G-8) and configured to receive a reflected opticalsignal produced by a mirror of the second mirror group (e.g., mirror160G) and transmit the reflected optical signal to the optical receiver.In some embodiments, one or more optical receivers of the first outeroptical receiver group (e.g., optical receivers 120A-1 to 120A-4 and120C-1 to 120C-4) or the second outer optical receiver group (e.g.,optical receivers 120G-5 to 120G-8) may serve in this way as an outputof a neural network including the photonic neural component 100. Forexample, in a case where the waveguide architecture shown in FIG. 7represents a photonic neural component 100 that is a complete neuralnetwork, the optical receiver chip 120C may server as an output of theneural network.

In place of transmitting waveguides 150A-1 to 150A-4, 150C-1 to 150C-4,and 150G-5 to 150G-8, the waveguide architecture of FIG. 7 insteadincludes input waveguides 730A-1 to 730A-4, 730C-1 to 730C-4, and 730G-5to 730G-8, divided into first input waveguides 730A-1 to 730A-4 and730C-1 to 730C-4 associated with the first ring and second inputwaveguides 730G-5 to 730G-8 associated with the second ring. (Due tolimited space, only input waveguides 730C-1 to 730C-4 are givenreference numbers in FIG. 7.) The first input waveguides 730A-1 to730A-4 and 730C-1 to 730C-4 may be formed on the board such that atleast one of the first input waveguides (e.g., first input waveguide730C-3) crosses at least one of the inter-node waveguides of the firstring (e.g., inter-node waveguide 130-4) with a core of one of thecrossing waveguides passing through a core or a clad of the other. Eachfirst input waveguide (e.g., 730C-3) may be connected to outside thefirst ring and configured to receive an optical signal from outside thefirst ring and transmit the received optical signal to an inter-nodewaveguide of the first ring (e.g., 130-3) via a multiplexer of the firstmultiplexer group (e.g., multiplexer 140C). Similarly, the second inputwaveguides 730G-5 to 730G-8 may be formed on the board such that atleast one of the second input waveguides (e.g., second input waveguide730G-7) crosses at least one of the inter-node waveguides of the secondring (e.g., inter-node waveguide 130-8) with a core of one of thecrossing waveguides passing through a core or a clad of the other. Eachsecond input waveguide (e.g., 730G-7) may be connected to outside thesecond ring and configured to receive an optical signal from outside thesecond ring and transmit the received optical signal to an inter-nodewaveguide of the second ring (e.g., 130-7) via a multiplexer of thesecond multiplexer group (e.g., multiplexer 140G).

Each of the optical transmitters of the first outer optical transmittergroup (e.g., optical transmitters 110A-1 to 110A-4 and 110C-1 to 110C-4)may be optically connected to a first input waveguide of the pluralityof first input waveguides (e.g., 730A-1 to 730A-4 and 730C-1 to 730C-4)and configured to emit an optical signal to be transmitted by the firstinput waveguide. Similarly, each of the optical transmitters of thesecond outer optical transmitter group (e.g., optical transmitters110G-5 to 110G-8) may be optically connected to a second input waveguideof the plurality of second input waveguides (e.g., second inputwaveguides 730G-5 to 730G-8) and configured to emit an optical signal tobe transmitted by the first input waveguide. That is, each second inputwaveguide (e.g., second input waveguide 730G-5, 730G-6, 730G-7, or730G-8) may be optically connected to an optical transmitter of thesecond outer optical transmitter group (e.g., optical transmitter110G-5, 110G-6, 110G-7, or 110G-8) and configured to receive an opticalsignal emitted from the optical transmitter and transmit the receivedoptical signal to an inter-node waveguide of the second ring (e.g.,inter-node waveguide 130-5, 130-6, 130-7, or 130-8) via a multiplexer ofthe second multiplexer group (e.g., multiplexer 140G). In someembodiments, one or more optical transmitters of the first outer opticaltransmitter group (e.g., optical transmitters 110A-1 to 110A-4 and110C-1 to 110C-4) or the second outer optical transmitter group (e.g.,optical transmitters 110G-5 to 110G-8) may serve in this way as an inputof a neural network including the photonic neural component 100. Forexample, in a case where the waveguide architecture shown in FIG. 7represents a photonic neural component 100 that is a complete neuralnetwork, the optical transmitter chip 110C may server as an input of theneural network.

In place of intra-node signal lines 190A-1 to 190A-4, 190C-1 to 190C-4,and 190G-5 to 190G-8, the waveguide architecture of FIG. 7 insteadincludes inter-ring intra-node signal lines 740AG-1 to 740AG-4 and740GA-5 to 740GA-8, signal lines connected to transmitter chip 110C andreceiver chip 120C having been completely omitted in this example toprovide an example of inputs and outputs of a neural network asdescribed above. (Due to limited space, only inter-ring intra-nodesignal lines 740AG-1 to 740AG-4 are given reference numbers in FIG. 7.Note that, by arbitrary convention, the order of letter suffices AG orGA refers to the direction from receiver chip to transmitter chip, whilethe number suffixes -1 to -4 or -5 to -8 refer to correspondinginter-node waveguides 130-1 to 130-4 or 130-5 to 130-8 of the ring ofthe receiver chip.) Each inter-ring intra-node signal line (e.g.,inter-ring intra-node signal line 740AG-1) may be connected to anoptical receiver of the first outer optical receiver group (e.g.,optical receiver 120A) and an optical transmitter of the second outeroptical transmitter group (e.g., optical transmitter 110G) andconfigured to receive an electrical signal representing a power of anoptical signal received by the optical receiver and transmit theelectrical signal to the optical transmitter, thereby connecting theoptical receiver and the optical transmitter to form an input and anoutput of a neuron. Similarly, each inter-ring intra-node signal line(e.g., inter-ring intra-node signal line 740GA-5) may be connected to anoptical transmitter of the first outer optical receiver group (e.g.,optical transmitter 110A) and an optical receiver of the second outeroptical receiver group (e.g., optical receiver 120G) and configured toreceive an electrical signal representing a power of an optical signalreceived by the optical receiver and transmit the electrical signal tothe optical transmitter, thereby connecting the optical receiver and theoptical transmitter to form an input and an output of a neuron. In otherwords, by the use of inter-ring intra-node signal lines, opticalreceivers of the first ring may be connected to optical transmitters ofthe second ring and optical receivers of the second ring may beconnected to optical transmitters of the first ring, thereby forminginter-ring nodes that may function as neurons connecting the rings. Inthis way, an arbitrary number of transmitters and receivers may beassembled across an arbitrary number of rings to scale the photonicneural component 100 or a neural network comprising the photonic neuralcomponent 100. Such scaling can include assembling rings into anarbitrary number of larger, higher-order rings or other structures,which may themselves be assembled into even larger, higher-order ringsor other structures, and so on, to form a super-loop or super-ring. Forexample, if the two rings shown in FIG. 7 are regarded as first-orderrings, a series of such first-order rings can be connected in a row thatbends in on itself to form a larger second-order ring. Such second-orderring may then be connected to other second-order rings in the same wayand so on. All such connections can be accomplished, for example, byinput and output waveguides as shown in FIG. 7.

FIG. 8 shows an example diagram of a waveguide architecture for aphotonic neural component 100 according to an embodiment of theinvention. In FIG. 8, a first plurality of first-order rings 810 areconnected in a row that bends in on itself to form a larger second-orderring, represented by the large ring including eight first-order rings810 on the left-hand side of the figure. A second plurality offirst-order rings 810 are connected in a similar row that bends in onitself to form a larger second-order ring, represented by the large ringincluding eight first-order rings 810 on the right-hand side of thefigure. Connections (shown as double-lines) are shown between thefirst-order rings 810, including one example connection connecting thetwo second-order rings. Each of the first-order rings 810 having twoconnections may be structured as the first (left-most) ring of FIG. 7,while each of the first-order rings 810 having three connections may bestructured similarly to the first (left-most) ring of FIG. 7 but with anadditional pair of transmitter chip 110 and receiver chip 120 moved fromthe inner group (containing chips 110/120 B and D in FIG. 7) to theouter group (containing chips 110/120 A and C in FIG. 7). Each of theconnections in FIG. 8 thus may contain waveguides and outertransmitter/receiver chip pairs of each of the connected first-orderrings 810, similar to the transmitter/receiver chips 110/120 A and G inFIG. 7. The left-most protruding connection in FIG. 8 may serve asinput/output for the pair of second-order rings shown in FIG. 8 (similarto the transmitter/receiver chips 110/120C and connected waveguides inFIG. 7). The second-order rings of FIG. 8 may be connected intothird-order or higher rings to scale the photonic neural component 100or a neural network comprising the photonic neural component 100.

In the above description, the output waveguides (e.g., 710C-1), inputwaveguides (e.g., 730-1), and inter-ring intra-node signal lines (e.g.,740AG-1) are referred to by different names than the receivingwaveguides (e.g., 170D-1), transmitting waveguides (e.g., 150D-1), andintra-node signal lines (e.g., 190H-5), respectively. However, apartfrom their relationship with the first and second rings, the outputwaveguides, input waveguides, and inter-ring intra-node signal lines maybe regarded as examples of receiving waveguides, transmittingwaveguides, and intra-node signal lines, respectively, and may have thesame respective structures. Therefore, throughout this disclosure, anydescription of receiving waveguides, transmitting waveguides, andintra-node signal lines may apply equally to output waveguides, inputwaveguides, and inter-ring intra-node signal lines, respectively.

In FIGS. 1, 3, 7, and 8 and throughout this description, reference ismade to a photonic neural component 100. The term “photonic neuralcomponent” and the corresponding reference number “100” in the drawingsmay refer to any component or combination of components of the waveguidearchitecture described throughout this disclosure, e.g., the entirety ofFIG. 1, 3, 7, or 8, a portion of FIG. 1, 3, 7, or 8, a variation and/orexpansion of FIG. 1, 3, 7, or 8, or any portion, variation, and/orexpansion of any embodiment of the waveguide architecture described inthis disclosure and not specifically depicted in the drawings, includingan entire neural network. A photonic neural component 100 or neuralnetwork may also include or be connected to some means of adjusting thepower of the emitted optical signals of the optical transmitters and/orthe sensitivity of the optical receivers, in order to adjust the balanceof the neural network. Adjustment parameters can be stored in a memory.Such means may include, for example, a computer connected to thephotonic neural component 100 or neural network. Such a computer mayfurther provide any practical functionality of the photonic neuralcomponent 100 or neural network, e.g., running a computer program thatuses neural computing at least in part or cooperates with neuralcomputing, varying the weights of the filters 180 (including outputfilters 720), varying reflection coefficients of the mirrors 160,issuing requests to emit optical signals from the optical transmitters,e.g., initial optical signals having instructed power, monitoring andreading the power of optical signals received by the optical receiversand returning the values to a computer program, etc. The computer may,for example, check that the same power level can be measured at alloptical receivers when optical signals having the same power areinstructed to be emitted by the optical transmitters and the sameweights are set to all filters, and the computer may make adjustmentsaccordingly.

As can be understood from this disclosure, the features of the photonicneural component 100 and related embodiments make it possible to avoidthe drawbacks associated with conventional techniques. Using thewaveguide architecture shown and described herein, a photonic neuralcomponent 100 can support photonic spike computing by optical signaltransmission with low loss via waveguides formed so as to cross oneanother on a board, e.g., a printed circuit board. The disclosedwaveguide architecture can therefore allow for design flexibility (e.g.,layout, materials, etc.) while lifting the speed restriction of theconventional electronic approach.

While the embodiment(s) of the present invention has (have) beendescribed, the technical scope of the invention is not limited to theabove described embodiment(s). It is apparent to persons skilled in theart that various alterations and improvements can be added to theabove-described embodiment(s). It is also apparent from the scope of theclaims that the embodiments added with such alterations or improvementscan be included in the technical scope of the invention.

What is claimed is:
 1. A photonic neural component comprising: aplurality of optical transmitters; a plurality of optical receivers; aplurality of inter-node waveguides formed on a board; a plurality ofmultiplexers formed on the board, each multiplexer configured tomultiplex an input optical signal onto an inter-node waveguide of theplurality of inter-node waveguides; a plurality of transmittingwaveguides formed on the board such that at least one transmittingwaveguide crosses at least one inter-node waveguide with a core of onecrossing waveguide passing through a core or a clad of another crossingwaveguide, each transmitting waveguide optically connected to an opticaltransmitter of the plurality of optical transmitters and configured toreceive an optical signal emitted from the optical transmitter andtransmit the optical signal to an inter-node waveguide of the pluralityof inter-node waveguides via a multiplexer of the plurality ofmultiplexers; a plurality of mirrors formed on the board, each mirrorconfigured to partially reflect the optical signal propagating on theinter-node waveguide of the plurality of inter-node waveguides toproduce a reflected optical signal; a plurality of receiving waveguidesformed on the board such that at least one receiving waveguide crossesthe at least one inter-node waveguide with a core of one crossingwaveguide passing through a core or a clad of another crossingwaveguide, each receiving waveguide optically connected to an opticalreceiver of the plurality of optical receivers and configured to receivethe reflected optical signal produced by a mirror of the plurality ofmirrors and transmit the reflected optical signal to the opticalreceiver; and a plurality of filters formed on the board, each filterconfigured to apply a weight to the reflected optical signal produced bythe mirror of the plurality of mirrors before the reflected opticalsignal is transmitted to the optical receiver by the at least onereceiving waveguide that receives the reflected optical signal.
 2. Thephotonic neural component of claim 1, wherein: the plurality of opticaltransmitters include a first optical transmitter to emit a first opticalsignal at a first wavelength and a second optical transmitter to emit asecond optical signal at a second wavelength different from the firstwavelength; and the plurality of inter-node waveguides includes aninter-node waveguide to propagate the first optical signal at the firstwavelength and the second optical signal at the second wavelength. 3.The photonic neural component of claim 2, wherein the plurality ofmirrors includes at least one mirror having a reflection coefficientdependent on wavelength.
 4. The photonic neural component of claim 3,wherein the plurality of filters includes a spectral filter having anapplied weight dependent on the wavelength.
 5. The photonic neuralcomponent of claim 1, wherein the plurality of multiplexers includes amultiplexer having an entrance mirror and a y-shaped waveguide structureconnected by a first entrance arm and an exit arm to the inter-nodewaveguide onto which the multiplexer multiplexes the input opticalsignal, the entrance mirror configured to receive, as the input opticalsignal, an optical signal transmitted by a transmitting waveguide of theplurality of transmitting waveguides and reflect the input opticalsignal to produce a reflected optical signal that enters a secondentrance arm of the y-shaped waveguide structure and joins an opticalsignal propagating on the inter-node waveguide where the second entrancearm meets the first entrance arm of the y-shaped waveguide structure. 6.The photonic neural component of claim 1, wherein the plurality offilters includes an exchangeable filter that can be exchanged to changethe weight.
 7. The photonic neural component of claim 1, wherein theplurality of filters includes a variable filter whose transparency canbe varied to change the weight.
 8. The photonic neural component ofclaim 1, further comprising a plurality of semiconductor chips mountedon the board, each of the plurality of semiconductor chips including atleast one optical transmitter or at least one optical receiver.
 9. Thephotonic neural component of claim 8, wherein: the plurality ofsemiconductor chips includes optical transmitter chips and opticalreceiver chips, each of the optical transmitter chips including one ormore of the plurality of optical transmitters and each of the opticalreceiver chips including one or more of the plurality of opticalreceivers; and the optical transmitter chips include a first opticaltransmitter chip whose one or more optical transmitters emit firstoptical signals at a first wavelength and a second optical transmitterchip whose one or more optical transmitters emit second optical signalsat a second wavelength different from the first wavelength.
 10. Thephotonic neural component of claim 9, wherein: each of the opticaltransmitter chips includes a same number of optical transmitters; eachof the optical receiver chips includes a same number of opticalreceivers; a number of optical transmitters included in each of theoptical transmitter chips is the same as a number of optical receiversincluded in each of the optical receiver chips; and a number ofinter-node waveguides connected to each of the optical transmitter chipsvia the plurality of transmitting waveguides is the same as the numberof optical transmitters included in each of the optical transmitterchips and the number of optical receivers included in each of theoptical receiver chips.
 11. The photonic neural component of claim 8,wherein: each of the plurality of semiconductor chips is positioned suchthat the at least one optical transmitter included in a semiconductorchip or the at least one optical receiver included in the semiconductorchip faces the board; the plurality of transmitting waveguides areconnected to the plurality of optical transmitters via entry mirrorsconfigured to redirect light from a direction perpendicular to the boardto a direction parallel to the board; and the plurality of receivingwaveguides are connected to the plurality of optical receivers via exitmirrors configured to redirect the light from the direction parallel tothe board to the direction perpendicular to the board.
 12. The photonicneural component of claim 8, further comprising: a plurality ofintra-node signal lines, each intra-node signal line connected to arespective optical receiver of the plurality of optical receivers and arespective optical transmitter of the plurality of optical transmittersand configured to receive an electrical signal representing a power ofan optical signal received by the optical receiver and transmit theelectrical signal to the optical transmitter, thereby connecting theoptical receiver and the optical transmitter to form an input and anoutput of a neuron.
 13. The photonic neural component of claim 12,wherein for each of the plurality of optical receivers connected to anoptical transmitter via an intra-node signal line, the plurality ofmirrors includes at least one mirror whose reflected optical signal istransmitted to the optical receiver and whose reflection coefficient issubstantially zero for a wavelength of the optical signal emitted by theoptical transmitter.
 14. The photonic neural component of claim 1,wherein the plurality of inter-node waveguides, the plurality oftransmitting waveguides, and the plurality of receiving waveguides aremade of polymer in a single layer of the board.
 15. The photonic neuralcomponent of claim 1, wherein the plurality of optical transmitters aredivided into differential pairs in which a first optical transmitter ofa differential pair emits a variable optical signal while a secondoptical transmitter of the differential pair emits a reference opticalsignal.
 16. The photonic neural component of claim 15, furthercomprising a plurality of semiconductor chips mounted on the board, eachof the plurality of semiconductor chips including one or more of thedifferential pairs.
 17. The photonic neural component of claim 16,wherein each of the plurality of semiconductor chips includes two ormore of the differential pairs.
 18. The photonic neural component ofclaim 1, wherein: the plurality of inter-node waveguides includes afirst ring having two or more inter-node waveguides arranged asconcentric loops; the plurality of optical transmitters includes a firstinner optical transmitter group having two or more optical transmittersdisposed inside the first ring; and the plurality of optical receiversincludes a first inner optical receiver group having two or more opticalreceivers disposed inside the first ring.
 19. The photonic neuralcomponent of claim 18, wherein: the plurality of mirrors includes afirst mirror group, each mirror of the first mirror group configured topartially reflect an optical signal propagating on an inter-nodewaveguide of the first ring to produce the reflected optical signal; andthe photonic neural component further comprises a plurality of firstoutput waveguides formed on the board such that at least one firstoutput waveguide crosses at least one inter-node waveguide of the firstring with a core of one of a crossing waveguide passing through a coreor a clad of another crossing waveguide, each first output waveguideconnected to outside the first ring and configured to receive thereflected optical signal produced by a first mirror of the first mirrorgroup and transmit the reflected optical signal to outside the firstring.
 20. The photonic neural component of claim 19, further comprisinga first output filter formed on the board, the first output filterconfigured to apply the weight to the reflected optical signal producedby the mirror of the plurality of mirrors before the reflected opticalsignal is transmitted to outside the first ring by the first outputwaveguide that receives the reflected optical signal.
 21. The photonicneural component of claim 20, wherein the plurality of optical receiversincludes a first outer optical receiver group having two or more opticalreceivers disposed outside the first ring, each of the optical receiversof the first outer optical receiver group connected to a first outputwaveguide of the plurality of first output waveguides and configured toreceive the reflected optical signal transmitted by the first outputwaveguide.
 22. The photonic neural component of claim 21, wherein: theplurality of inter-node waveguides includes a second ring having two ormore inter-node waveguides arranged as concentric loops; the pluralityof optical transmitters includes a second inner optical transmittergroup having two or more optical transmitters disposed inside the secondring and a second outer optical transmitter group having two or moreoptical transmitters disposed outside the second ring; the plurality ofoptical receivers includes a second optical receiver group having two ormore optical receivers disposed inside the second ring; the plurality ofmultiplexers includes a second multiplexer group, each multiplexer ofthe second multiplexer group configured to multiplex the input opticalsignal onto an inter-node waveguide of the second ring; the photonicneural component further comprises a plurality of second inputwaveguides formed on the board such that at least one second inputwaveguide crosses at least one of the inter-node waveguides of thesecond ring with a core of one crossing waveguide passing through a coreof a clad of another crossing waveguide, each second input waveguideoptically connected to an optical transmitter of the second outeroptical transmitter group and configured to receive the optical signalemitted from the optical transmitter and transmit the optical signal toan inter-node waveguide of the second ring via a multiplexer of thesecond multiplexer group; and the photonic neural component furthercomprising a plurality of intra-node signal lines, wherein the pluralityof intra-node signal lines includes a plurality of inter-ring intra-nodesignal lines, each inter-ring intra-node signal line connected to anoptical receiver of the first outer optical receiver group and anoptical transmitter of the second outer optical transmitter group andconfigured to receive an electrical signal representing a power of theoptical signal received by the optical receiver and transmit theelectrical signal to the optical transmitter, thereby connecting theoptical receiver and the optical transmitter to form an input and anoutput of a neuron.
 23. The photonic neural component of claim 18,wherein: the plurality of multiplexers includes a first multiplexergroup, each multiplexer of the first multiplexer group configured tomultiplex the input optical signal onto an inter-node waveguide of thefirst ring; and the photonic neural component further comprises aplurality of first input waveguides formed on the board such that atleast one first input waveguide crosses at least one inter-nodewaveguide of the first ring with a core of one crossing waveguidepassing through a core or a clad of another crossing waveguide, eachfirst input waveguide connected to outside the first ring and configuredto receive an optical signal from outside the first ring and transmitthe optical signal to an inter-node waveguide of the first ring via amultiplexer of the first multiplexer group.
 24. The photonic neuralcomponent of claim 23, wherein the plurality of optical transmittersincludes a first outer optical transmitter group having two or morefirst optical transmitters disposed outside the first ring, each of thefirst optical transmitters of the first outer optical transmitter groupoptically connected to a first input waveguide of the plurality of firstinput waveguides and configured to emit an optical signal to betransmitted by the first input waveguide.
 25. The photonic neuralcomponent of claim 24, wherein: the plurality of inter-node waveguidesincludes a second ring having two or more inter-node waveguides arrangedas concentric loops; the plurality of optical transmitters includes asecond inner optical transmitter group having two or more opticaltransmitters disposed inside the second ring; the plurality of opticalreceivers includes a second optical receiver group having two or moreoptical receivers disposed inside the second ring and a second outeroptical receiver group having two or more optical receivers disposedoutside the second ring; the plurality of mirrors includes a secondmirror group, each mirror of the second mirror group configured topartially reflect an optical signal propagating on an inter-nodewaveguide of the second ring to produce a reflected optical signal ofthe second ring; the photonic neural component further comprises aplurality of second output waveguides formed on the board such that atleast one second output waveguide crosses at least one inter-nodewaveguide of the second ring with a core of one crossing waveguidepassing through a core or a clad of another crossing waveguide, eachsecond output waveguide optically connected to an optical receiver ofthe second outer optical receiver group and configured to receive thereflected optical signal of the second ring produced by a mirror of thesecond mirror group and transmit the reflected optical signal of thesecond ring to the optical receiver; and the plurality of intra-nodesignal lines includes a plurality of inter-ring intra-node signal lines,each inter-ring intra-node signal line connected to an opticaltransmitter of the first outer optical receiver group and an opticalreceiver of the second outer optical receiver group and configured toreceive an electrical signal representing a power of an optical signalreceived by the optical receiver and transmit the electrical signal tothe optical transmitter, thereby connecting the optical receiver and theoptical transmitter to form an input and an output of a neuron.